Bacterioferritin

Bacterioferritin (Bfr) is an oligomeric protein containing both a binuclear iron centre and haem b. The tertiary and quaternary structure of Bfr is very similar to that of ferritin. The physiological functions of BFR, which may be other than just iron uptake, are not clear. Bfr forms a roughly spherical, hollow shell from 24 identical subunits, incorporating 12 haem groups. Iron is stored as a hydrated ferric oxide mineral in its central cavity (about 80 Å diameter). The overall complex has cubic (432) symmetry. Each subunit includes a binuclear metalbinding site (the diiron site) linking together the four major helices of the subunit, which has been identified as the ferroxidase active site. Frolow, F., Kalb, A. J. & Yariv, J. (1994). Structure of a Unique Twofold Symmetrical Heme-Binding Site. Nature Structural Biology 1, 453–460.